Method for recovering oil from used lubricants

ABSTRACT

A method for recycling used lubricant oils into clean oils including mixing the used lubricant oil with a low and/or non-polar hydrocarbon solvent, like an aliphatic or oxygenated compound of 4-7 carbons linear molecule, and subjecting the mixture used lubricant/solvent(s) to at least one filtration with a medium of about 50,000 Daltons or less and the mixture is separated from the solid flocculated material.

CROSS REFERENCE TO RELATED APPLICATION

This application is related to and claims the benefit of U.S. Provisional Patent Application Ser. No. 61/551,748 filed on 26 Oct. 2011, the contents of which are herein incorporated by reference in their entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention concerns a method for recovering oils from a used lubricant. The method of the invention considers different steps in which the oil to be recovered is subjected to physical separations and suitable chemical reactions in order to produce recovered oil whose properties are identical or similar to those from non-used newly refined oil.

BACKGROUND OF THE INVENTION

In the modern industrialized world it is estimated that at least 40% of all used lubricant oils are released into the environment. Lubricant oils are present in a multitude of industrial and consumer products, like crankcase oil, hydraulic oil, transmission oil, mechanical cutting oils, aluminum rolling oils and oil-well drilling muds. Used lubricant oils can cause considerable damage to the environment due to their high content of pollutants, additives and oxidation products from previous uses. However, the need for lubricants increases due to their importance in reducing friction, surface fatigue, heat generation, operating noise and vibrations.

Strict regulations regarding lubricant oils disposal have been passed in the last decades in most countries as even small amount of lubricant can contaminate a large amount of water. These regulations establish the threshold level of lubricant oil that may be present in waste streams so the environmental impact is reduced. In order to comply with the requirements companies spend millions of dollars in treating their waste waters.

Another possibility for disposing of lubricant oils is by using them as fuel. However, this possibility has also been regulated on account of the relatively high level of additives present. Burning used lubricant oils generates both airborne carcinogen pollutants like dioxins and ash rich in toxic materials, mainly heavy metal compounds. Due to the toxic materials, used lubricant oils burning takes place in specialized facilities comprising expensive technologies to remove airborne pollutants and handle the toxic ash.

There are some expensive technologies, both in investment and operation, like wiped film evaporation, hydrogenation or Supercritical Propane extraction, which allows to recycle the oil in these lubricants. They are limited to very large facilities due to their economy of scale, both in infrastructure costs and personnel requirements due to operational complexity.

Finally, prior to this invention, the possibility to use filtration to remove contaminants from lubricant oils was limited to the use of high temperatures to reduce viscosity, which damaged both the oil and the filtration media. The best results obtained before this invention was a filtration with 0.05 microns, approximately equivalent to 750,000 Daltons, at a temperature no less than 200 F, via vibro-filtration, and obtained no more than 65% of recycled oil.

Due to the environmental negative impact, expensive costs of treatment and disposal and, on the other hand, the increasing uses of lubricants, it is important to devise new and more accessible methods for recycling used lubricant oils. In this regard, the invention, therefore, provides a method for recovering used oil to produce oil capable of being reused as, for example, lubricant, fuel, or hydraulic oil.

The invention further provides an oil recovering method for producing oil comparable in properties to newly refined oil.

BRIEF SUMMARY OF THE INVENTION

The method of this invention comprises the following steps:

Mixing the used lubricant with a hydrocarbon solvent which is not miscible with water, either a very low polar, a non-polar hydrocarbon solvent, or mixtures thereof. Since polar compounds won't dissolve in the low or non-polar solvent, the polar pollutants present in the used lubricant will be separated via flocculation, thus facilitating the separation steps by filtration. Also a polar solvent, like water or glycol, can be added to promote contaminants flocculation. If flocculation of contaminants is massive a previous separation step may be included before the next step.

In a second step the mixture used lubricant/solvent(s) is filtered with a medium of about 50,000 Daltons or less, more preferably a medium of about 30,000 Daltons, preferably of PVDF material. Generally, a first filtration will suffice for the purposes of the present invention. However, if required, the resulting used lubricant-rich filtrate undergoes a second filtration with a medium of about 7,000 Daltons or less, more preferably a medium of about 3,000 Daltons. The mixture of second filtration separates into two phases: a used lubricant-rich filtrate and a solid portion. The filtration method used for the two consecutive filtrations depends on the nature and condition of the used oil to be recovered. All filtrations methods are suitable; however, it is preferable to use a filtration method based on vibratory filtration mediums.

The method of the invention may comprise the following independent optional steps:

Before mixing the used lubricant with the very low polar or non-polar hydrocarbon solvent, or mixtures thereof, it might be heated to about 130° C. in order to remove pollutants—including water—having a boiling point lower than the boiling point of the solvents to be employed in the next steps. If after this treatment the used lubricant is hot, it is allowed to cool to room temperature before mixing it with the very low polar or non-polar hydrocarbon solvent.

Before mixing the used lubricant with the very low polar or non-polar hydrocarbon solvent it might be exposed to chemical reactions using acidic substances, bases, a powerful oxidant agent like ozone, or mixtures thereof. This way structural modification would be achieved to increase both the polarity of some compounds or their molecular bond cleavage. This can be done at room temperature or at a temperature not higher than 130° C. According to the lubricant source the stimulus of ultrasound vibration and/or microwave irradiation could be also used during the process. The acid can be strong (like sulfuric, hydrochloric or nitric acid) or weak (like formic or acetic); the base has to be strong (like sodium or potassium hydroxides).

After filtering the mixture of used lubricant/solvent(s) with a medium of about 50,000 Daltons or less, the low or non-polar solvent might be recuperated via evaporation from the permeate and the solid phases obtained in previous filtration.

DETAILED DESCRIPTION

The method of this invention is applicable to any used lubricant or used oil. This includes used oils from domestic uses, industrial facilities and others in which the major constituent is hydrocarbon oil. The term oil refers to petroleum-based oils, synthetic oils or similar types thereof. The method comprises two main steps:

-   -   1. Enhancement of the difference of polarity and viscosity         between the oil and its contaminants via solvent dilution and         chemical reactions     -   2. Separation of the oil and its contaminants

Enhancement of the Difference of Polarity and Viscosity Between the Oil and its Contaminants

The used lubricant, preferably at room temperature, is mixed with solvents not miscible (non-polar) and/or slightly miscible (low-polar) with water and/or mixtures thereof. Examples of the non-polar solvents are aliphatic or oxygenated compound of 4-7 carbons linear molecule, preferably, non-polar solvents are n-pentane, n-hexane, n-heptane; and examples of the low polar solvent are 1-butanol, methyl-ethyl-ketone and 1-pentanol. More preferably, the non-polar solvent is n-heptane and the low-polar solvent is 1-butanol. Since polar compounds won't dissolve in these low/non-polar solvents, the polar pollutants present in the oil will be separated, thus facilitating the separation and filtering steps. Other advantages of adding the low/non-polar solvents are the reduction of the oil viscosity so it can be filtered with lower porosity. The ratio of oil to solvent is between 1:1 and 1:5 in volume, preferably, the ratio is between 1:1 and 1:2 in volume. More preferably, the ratio of oil to non-polar solvent is 1:1 in volume; and 1:2 in volume for the low-polar solvent. In the case of used crankcase and hydraulic rolling oil, 1-butanol is preferred, in the case of used cutting oil, aluminum rolling oil and drilling muds, n-heptane is preferred.

In an independent optional step, the used lubricant is heated at temperatures of about 130° C. before mixing it with the very low polar or non-polar hydrocarbon solvent. This heating step helps to remove pollutants having a boiling point lower than the boiling point of the solvents to be employed in successive steps. The term “pollutants”, in this context, includes water and any other compound that might be present as additive due to the previous use of the used oil to be treated. Carbon particles, resins, oxides, etc are considered as pollutants as well. As the low boiling point hydrocarbons are removed, the result is a used lubricant or oil substantially free of low boiling contaminants.

In another independent optional step, the polarity of its contaminants may be increased in an optional step comprising subjecting the used lubricant to chemical reactions with an acid, a base, ozone, or mixtures thereof can be included before mixing it with the low or non-polar solvent. More particularly, the used lubricant or oil can be exposed to either: a strong acid like sulfuric, nitric or hydrochloric acids, a weak acid like formic or acetic acid, a strong base like sodium hydroxide, or a powerful oxidant agent like ozone. The reaction can be performed at room or a little higher temperature, and accordingly can be stimulated with ultrasound vibration and/or microwave emissions. Hydroxides can be added in a ratio of 1 to 2% w/w, preferably 1%; and ozone in a ratio of 1,000 to 2,000 ppm, preferably 2,000 ppm. In this step, contaminant molecules can experience several types of modifications: hemolytic and heterolytic cleavage, oxidations, substitutions, additions and neutralization. The preferred reactant in this step is sodium hydroxide at 150° Celsius degrees during 30 minutes.

In yet another optional step, a highly polar solvent can be added to the mixture in order to facilitate the flocculation of the contaminants. Examples of these polar solvents can be water or ethylene glycol. These solvents can only be added if a non-polar solvent is used. In case water is used, the ratio is determined by the disposal restrictions of the contaminants, but in no case has been observed that more than a 1:1 ratio is needed. In case ethylene glycol is used a ratio of no more than 2% v/v is used, a ratio of 1% is preferred. For example, in the case of used crankcase and hydraulic oil, ethylene-glycol is preferred; in the case of used well drilling muds, water is preferred.

In yet another independent optional step, and only in case the flocculation induced is significant, the oil/solvent(s) mixture can be centrifuged to separate a significant amount of the original contaminants. These contaminants will flocculate as highly viscous paste, which can represent between 4 to 10% of the original mass. The remaining lubricant will be significantly free of contaminants, especially but not exclusively of the resin type.

Separation of the Oil and its Contaminants

The mixture used lubricant/solvent(s) is filtered with a medium of about 50,000 Daltons or less, more preferably a medium of about 30,000 Daltons. The mixture of this filtration separates into two phases: a used lubricant or oil-rich filtrate and a solid portion. The solid portion is discarded or treated to recover the solvent retained in the solid particles. Generally, a first filtration will suffice for the purposes of the present invention and the procedure will continue as described below. However, if required, the used lubricant or oil-rich filtrate undergoes a second filtration with a medium of about 7,000 Daltons or less, more preferably a medium of about 3,000 Daltons. The mixture of second filtration separates into two phases again: a used lubricant or oil-rich filtrate and a solid portion. The filtrate from the second filtration is recovered and the solid portion is discarded or, more preferably, the solid portion from the second filtration is mixed with an unfiltered batch of an oil/non-polar solvent mixture to undergo the first filtration. The filtration method used for the two consecutive filtrations depends on the nature and condition of the used oil to be recovered. All filtrations methods are suitable; however, it is preferable to use a filtration method based on vibratory filtration medium identical or similar to those disclosed in U.S. Pat. No. 4,952,317, U.S. Pat. No. 4,872,988 and U.S. Pat. No. 5,014,564. The frequency vibration of the vibratory filtration medium in both filtration steps is between 50 and 70 Hz. All parameters of the filtration: pressure, flow, porosity, membrane composition, vibration frequency, etc., are selected to promote the permeation of the hydrocarbon mix and the rejection of the polar mix, which couldn't happen without the proper settings.

An independent optional step, after the filtration, the filtrate is treated to remove the not miscible (non-polar) or slightly miscible (low-polar) solvent by boiling or filtration, preferably the filtrate is thermally treated. The solvent is thus recovered.

The outcome of the method of the invention, considering its optional steps if necessary, is used lubricant or oil whose hydrocarbon properties are identical o similar to those from new refined product.

The method of this invention is illustrated by the following examples.

Previous Technology

For illustrative purposes the following example has been included where a used lubricant is treated with a method according to the state of the art. Used oil from a diesel engine was heated to 110° C. The oil was filtered with a vibratory filtering medium of 0.05 microns (approx. 750,000 Daltons) at 60 Hz. The characteristics of the resulting lubricating oil are shown in the following table.

Recovered Parameter Units Used oil oil Mass % 100 65 Iron Ppm 86  7 Chromium Ppm 2 <1   Nickel Ppm <1   <1   Aluminum Ppm 8 <1   Lead Ppm 12  10  Copper Ppm 39  27  Tin Ppm <1   <1   Silver Ppm   0.3   0.2 Titanium Ppm <1   <1   Silicon Ppm 15  7 Boron Ppm 29  2 Sodium Ppm 70  1 Potassium Ppm <10    <10    Molybdenum Ppm 5 <5   Phosphorous Ppm 845  334  Zinc Ppm 846  267  Calcium Ppm 2614   84  Barium Ppm <10    <10    Magnesium Ppm 43  3 Antimony Ppm <30    <30    Vanadium Ppm <1   <1  

Example 1

Used lubricant oil from an auto mixed with n-hexane in an oil/n-hexane ratio of 1:1 at room temperature. The mixture was filtered with a vibratory filtering medium of 50,000 Daltons at 50 Hz. The characteristics of the resulting lubricating oil are shown in the following table. Blank spaces indicates that contaminants or pollutants concentration were below detection levels.

Used Recovered Parameter Units oil oil Mass % 100 85 Iron ppm 32 3 Aluminum ppm 5 — Copper ppm 113 10 Lead Ppm 8 — Sodium Ppm 12 — Silicon Ppm 9 1 Potassium Ppm 2 — Calcium Ppm 2206 13 Magnesium Ppm 51 — Boron Ppm 25 3 Phosphorus Ppm 1071 464 Molybdenum Ppm 21 — Zinc Ppm 1218 415

Example 2

Used lubricant oil from an auto engine was mixed with 1% of caustic soda (NaOH) and heated to 110° C. After cooled was mixed with n-hexane in an oil/n-hexane ratio of 1:1. The mixture was filtered with a vibratory filtering medium of 50,000 Daltons at 50 Hz. The characteristics of the resulting lubricating oil are shown in the following table. Blank spaces indicates that contaminants or pollutants concentration were below detection levels.

Used Recovered Parameter Units oil oil Mass % 100 89 Iron ppm 32 1 Aluminum ppm 5 — Copper ppm 113 12 Lead Ppm 8 — Sodium Ppm 12 5 Silicon Ppm 9 — Potassium Ppm 2 — Calcium Ppm 2206 9 Magnesium Ppm 51 4 Boron Ppm 25 1 Phosphorus Ppm 1071 364 Molybdenum Ppm 21 — Zinc Ppm 1218 15

Example 3

Used lubricant oil from a diesel engine was mixed with 1% of caustic soda (NaOH) and heated to 110° C. After cooled was mixed with 1-butanol in an oil/alcohol ratio of 1:2. The mixture was first centrifuged to remove precipitated asphalts and then filtered with a vibratory filtering medium of 30,000 Daltons at 50 Hz. The characteristics of the resulting lubricating oil are shown in the following table. Blank spaces indicates that contaminants or pollutants concentration were below detection levels.

Used Recovered Parameter Units oil oil Mass % 100 95 Iron ppm 42 2 Aluminum ppm 5 1 Chrome ppm 1 1 Copper ppm 110 10 Lead Ppm 9 0 Manganese Ppm 1 — Sodium Ppm 14 1 Silicon Ppm 7 1 Potassium Ppm 4 — Calcium Ppm 2746 5 Magnesium Ppm 45 2 Boron Ppm 24 1 Phosphorus Ppm 1100 187 Molybdenum Ppm 22 5 Zinc Ppm 1315 5 

1. A method for recycling used lubricant oils into clean oils comprising, mixing the used lubricant oil with a low and/or non-polar hydrocarbon solvent comprising an aliphatic or oxygenated compound of 4-7 carbons linear molecule, subjecting the mixture used lubricant/solvent(s) to at least one filtration with a medium of about 50,000 Daltons or less and the mixture is separated from the solid flocculated material.
 2. A method of claim 1, wherein the used lubricant is heated to about 130° C. before mixing it with the low and/or non-polar hydrocarbon solvent.
 3. A method of claim 1, wherein the contaminants in used lubricant are exposed to chemical reactions with either an acid, a base, ozone, or mixtures thereof before subjecting the mixture used lubricant/solvent(s) to at least one filtration.
 4. A method of claim 1, wherein the mixture of used lubricant/solvent(s) is also mixed with a high polar solvent, along with the low and/or non-polar hydrocarbon solvent.
 5. A method of claim 4, where the high polar solvent is water.
 6. A method of claim 4, where the high polar solvent is a short chain oxygenated hydrocarbon.
 7. A method of claim 6, wherein the short chain oxygenated hydrocarbon is ethylene glycol.
 8. A method of claim 1, wherein the mixture used lubricant/solvent(s) undergoes a second filtration with a medium of about 7,000 Daltons or less.
 9. A method of claim 8, wherein the mixture used lubricant/solvent(s) undergoes the second filtration with a medium of about 3,000 Daltons.
 10. A method of claim 1, wherein the filtration methods are based on a vibratory filtration medium where frequency is between 50 and 70 Hz.
 11. A method of claim 1, where the mixture used lubricant/solvent(s) undergoes at least one filtration with a medium of about 30,000 Daltons.
 12. A method of claim 1, wherein the lubricant oil undergoes a separation via centrifugation before subjecting the mixture of used lubricant/solvent(s) to the filtration step.
 13. A method for recycling used lubricant oils into lubricant bases comprising, heating the used lubricant to about 130° C. in order to remove pollutants having a boiling point lower than a boiling point of solvents to be employed, and then the oil is allowed to cool dawn to room temperature, exposing the contaminants in used lubricant to chemical reactions with either an acid, a base, ozone, or mixtures thereof, mixing the used lubricant with a low, non polar hydrocarbon solvent comprising an aliphatic or oxygenated compound of 4-7 carbons linear molecule, with a high polar solvent, or mixtures thereof, subjecting the mixture used lubricant/solvent(s) to at least one filtration with a medium of about 50,000 Daltons or less, and the mixture is separated from the solid flocculated material, treating the mixture thermally to remove the low/non-polar solvent added.
 14. A method of claim 13, wherein the mixture used lubricant/solvent(s) undergoes a second filtration with a medium of about 7,000 Daltons or less.
 15. A method of claim 14, wherein the mixture used lubricant/solvent(s) undergoes the second filtration with a medium of about 3,000 Daltons.
 16. A method of claim 13, wherein the filtration methods are based on a vibratory filtration medium where frequency is between 50 and 70 Hz.
 17. A method of claim 13, wherein the mixture used lubricant/solvent(s) undergoes at least one filtration with a medium of about 30,000 Daltons.
 18. A method of claim 13, wherein the lubricant oil undergoes a separation via centrifugation before subjecting the mixture of used lubricant/solvent(s) to the filtration step.
 19. A method of claim 18, where the high polar solvent is water.
 20. A method of claim 18, where the high polar solvent is a short chain oxygenated hydrocarbon.
 21. A method of claim 20, wherein the short chain oxygenated hydrocarbon is ethylene glycol. 